Patent GB-800234-A (GB)
Title: Improvements in or relating to the transmission of radar data
Inventor: THOMAS DAVID LANE
IPC: G01S7/00
Filed: 1955-10-07
Abstract: 800,234. Pulse modulation systems; radar. DECCA RECORD CO., Ltd. Jan. 4, 1957 [Oct. 7, 1955], No. 28694/55. Classes 40 (5) and 40 (7). Radar-data relay apparatus comprises means for generating a series of pulses of constant repetition rate and of amplitudes corresponding to target ranges, means for transmitting the series of pulses and a receiver for reconverting it into signals occurring at times representative of target ranges. In the first embodiment radar echo pulse video signals in a pulse recurrence period are converted into a series of short duration pulses marking the beginnings and the ends of the echoes; these derived pulses are stored on a storage-type cathode-ray (C.R.) tube and read off so as to produce a series of pulses of constant repetition period having amplitudes representing the ranges of the beginnings and the ends of the radar echoes. The receiver reverses this process to give video signals for direct application to a conventional radar display. The derived pulses are obtained from the video input by oppositely-polarized differentiators 11, 12 (see Fig. 1) and adder 13, and modulate a horizontal " write " scan from saw-tooth generator 16 triggered from generator 15 (frequency f) itself locked to the radar system pulse transmission. " Flip-flop " circuit 22 controlled from generator 15 so affects the " reading " and " writing " vertical shifts of the scanning beams of the storage C.R. tube 14 that writing takes place in two lines, one for each alternate scan, and reading takes place on the line not being written upon. Clock pulse generator 20, locked to generator 15, produces nf pulses per second, n. being twice the number of expected targets on any bearing; saw-tooth generator 21, triggered by the clock pulses, so controls the " reading " beam horizontal scan that it will cover one line in 1/nf scans of the " writing " beam. When the " reading " beam reaches the first pulse stored on a line the ensuing storage tube output stops generator 21 whose output voltage thus corresponds to the radar range of that stored pulse; and that pulse is erased. Generator 21 remains quiescent until the next clock pulse arrives, when a second traverse produces an output voltage proportional to the second stored pulse, i.e. the end of the first radar echo. These output voltages are held on capacitor 23 which is re-set by a circuit 24 controlled by clock pulses. A pulse proportional to the voltage on the holding capacitor is gated out by gate 26 triggered by clock pulses. A series of amplitude-modulated pulses of repetition period 1/nf are therefore produced and are transmitted from radio transmitter 28. When all the stored pulses on a line have been scanned, as ascertained by voltage comparator 27, a series of clock pulses of the same amplitude as the maximum possible under the above operations are produced until the end of the radar pulse repetition period. The " reading " process is then repeated on the other line trace on the storage tube, whose " writing " has just been completed. The received signals are detected and decoded by a reverse process to that described above, see Fig. 2, not shown, one output being a signal of frequency f fed to the radar display and the other output, corresponding to the original radar video input, modulating the radar display trace. In the second embodiment difference information only is transmitted. The coding and transmitting equipment, see Fig. 3, has a time delay between the input to coding unit 60 and the output from decoding unit 61 equal to one aerial scan period. Picture storage unit 62 adds the changes represented.by the output of the decoding unit to corresponding information from previous aerial scans, to build up signals corresponding to a complete radar picture. The coding equipment, see Fig. 4 ; includes aerial sweep frequency source 70, locked to the radar aerial rotation, which controls saw-tooth generator 71 enabling the radar data to be stored on a rectangular raster on storage C.R. tube 14. " Flip-flop " circuit 72 is provided so that the " writing " and " reading " beams are moved to the appropriate raster, the " reading beam beginning on a raster when half of it has been written. Unit 73 adds to the output of adder 13 pulses sufficiently strong to enable determination of additive and subtractive information. Conversion of information stored on C.R. tube 14 into amplitudemodulated pulses is carried out as in the first embodiment. At the receiver, see Fig. 5, decoded signals representing changes in the video signals for the radar-display are added in unit 83 which receives also part of the output from storage unit 84 so that after a time the output from unit 84 will represent the complete video radar information, fed to a conventional display unit.